LET'S STAY PHYSICAL: Deon Grant (right) is one Giants player who believes commissioner Roger Goodell's crackdown on helmet-to-helmet hits will take away from the game and lead to other career-ending injuries. Photo: EPA

The NFL’s crackdown on helmet-to-helmet hits has come under fire inside the Timex Performance Center, where the Giants do not believe that commissioner Roger Goodell has led with his head.

“Just tell us to stop hitting … put a flag on us and let us play flag football,” safety Deon Grant said. “If you teach how the NFL is telling us to play at Pop Warner, they’ll never get drafted because they’ll be soft. They’ll be questioned coming out of college. They may not even get a scholarship. ‘He doesn’t really want to tackle.’ ”

On and on it went, around the locker room.

“Insane,” Brandon Jacobs said, “just insane.”

Hey, fellas: CALM DOWN.

What we have here is a typical hysterical overreaction on the part of men who love when we refer to them as gladiators and warriors to what they believe is a league overreaction that threatens the very fabric and culture of their sport.

John Mara promises it doesn’t. And it won’t.

“I don’t think we’re changing the way the game is played,” Mara told The Post last night. “We’re just asking the players to be mindful that some of these vicious hits, particularly when they involve going to the head, have no place in the game.”

The Giants co-owner has been a member of the Competition Committee for a decade now.

“We’re not changing the rules,” Mara said. “The only time we do that is in the offseason after a lot of discussion and a lot of review of tape. All we’re saying is the rules are going to be enforced and the penalties are going to be harsher.

“They certainly don’t have to change the way they’ve been coached on this team. They’ve been coached to do it the right way.”

Mara conceded that because of the speed of the game, there will be invariably be incidental helmet-to-helmet hits (Jason Pierre-Paul on Zack Follett).

“I think the message the commissioner and the league are trying to send is you’re going to have to lower your strike zone a little bit and stay away from the head and neck area,” Mara said.

But both Grant and special teams captain Chase Blackburn worry the league will be trading concussions for career-ending ACL injuries.

“Would you rather that guy [Steelers’ linebacker James] Harrison went low — go straight at the dude’s knee, pop it out of its socket, and his career is over with?” Grant said. “Or you give him a concussion, and he could think about if he still wants to play this sport?”

If he still can remember who he is, that is.

The league isn’t asking the players to trade in their helmets and shoulder pads for tutus. The league is reminding them that the helmet is a life-threatening weapon.

“These rules aren’t being made by civilians like myself,” Mara said. “This is done with input from coaches and general managers, from people who have a lot of experience within the game.”

Major league Baseball umpires cannot read intent from a beanball pitcher, so the players are right when they argue that the zebras cannot read intent with 22 bodies flying around the field at warp speed. And they have a legitimate gripe over the excessive nature of Harrison’s $75,000 fine.

The players will have no choice but to adapt. Player safety trumps all.

“I don’t think it’s going to mean we’re going to play flag football from now on,” Mara said.

“All we’re saying is, ‘Just stay away from the head and just play by the rules.’ ”

Coach Tom Coughlin presented an instructional video yesterday to his team. “Whether they agree or disagree, they will listen to what the commissioner has to say,” the coach said.

Giants defenders were coached to lower the target in preseason.

“Not the aggressiveness,” Coughlin said.

Asked what he thought about John Madden’s idea to scrap helmets, Coughlin said: “We’d go back to when my uncle played and the cars pulled up to the side of the field and turned the lights on.”

Antrel Rolle and Keith Bulluck vow they will not change the way they play.

“I don’t know how you take violence out of a violent game,” Mathias Kiwanuka said. “Most guys do not intend to hit people with their helmets, it just happens and if you try to stop people from doing that you’re going to take a lot of things out of the game. You might as well just have everybody tag off on the person with the ball.”